1. Field of the Invention
The present invention relates to walk-throughs in a virtual space.
2. Related Background Art
An approach has been proposed in which a real space is photographed with an image pickup apparatus mounted on a moving body, and in accordance with the taken photography image data, the photographed real space is rendered into a virtual space by using a computer. For example, refer to “Building Image-Based Cybercities By Using Vehicle-Mounted Cameras,” by Endo, Katayama, Tamura, Hirose, Watanabe and Tanigawa (SINGAKU SOCIETY, PA-3-4, pp. 276-277, 1997), “Building Image-Based Cybercities By Using Vehicle-Mounted Cameras (2),—Generation Of Wide-Range Virtual Environment By Using Photorealistic Images—,” by Hirose, Watanabe, Tanigawa, Endo, Katayama and Tamura (Papers of Second Meeting of Japan Virtual Reality Society, pp. 67-70, 1997), and the like.
As an approach to photographing a real space with an image pickup apparatus mounted on a moving body, and in accordance with the taken photography image data, rendering the photographed real space into a virtual space by using a computer, conventional computer graphics techniques are utilized to realize a geometrical model of a real space in accordance with actually photographed image data. However, there are some limits in terms of correctness, precision, and fidelity to nature of the model. Instead of realizing a model, popular modern image-based rendering (IBR) techniques have been used in which a virtual space is expressed by using photographed images. IBR techniques are based upon photographed images so that a virtual space with a high fidelity to nature can be formed.
In order to configure walk-through by utilizing such IBR techniques, it is necessary to generate and present images at any respective position of an observer in a virtual space. In such a system, correspondence between each frame of photographed image data and its position in a virtual space is stored, and a corresponding frame is reproduced in accordance with the position and view direction of an observer in the virtual space.
In walk-through in such a virtual space, an observer is allowed to look at an image at each view position along a desired direction. To this end, an image at each view position is stored as a panoramic image which encompasses a wider area than the angle of view displayed when the image is reproduced. A proper panoramic image is selected in accordance with the view position and view direction of an observer in the virtual space, and a part of the image reproduced is displayed. For example, the panoramic image along the road on which a car which mounts an image pickup apparatus runs is recorded and reproduced. The observer can feel as if the observer gets in a car and travels along the road. After the observer arrives at an intersection and the observer selects another road different from the road that was previously displayed, the reproduced panoramic image group is changed to another panoramic image group to reproduce the image along a new path.
There are, however, some operational facets of conventional walk-through systems that can be improved.
Since allowable paths at an intersection are not displayed by using a figure such as an arrow and synthesizing the figure and a panoramic photographic image, a user is unable to distinguish between an allowable path and an unallowable path due to lack of photographic data.
With a conventional walk-through system, the motion of an observer on a path is limited to forward or backward motion. Advancement along a path in the view direction of the observer is regarded as forward motion. When the observer arrives at an intersection after the car had traveled on the path, a path nearest to the view direction of the observer is used as the next path. In this case, if a path having an angle of 90° or smaller relative to the forward direction of the path on which the car traveled is to be selected as the next path at the intersection, it is necessary to set the view direction to 90° or smaller relative to the forward direction. However, if the view direction is set to 90° or larger, the forward and backward directions are reversed, and the car moves away from the crossing. Therefore, in a conventional system, one is unable to continue along a view path having an angle of 90° or larger relative to the forward direction.